The manufacture of polyvinyl chloride sheet stock according to the "Luvitherm" method is conventional. (See, e.g., "Kunststoff Handbuch" [Plastics Manual] vol. II, Carl Hanser Publishers, Munich, 1963, part 1, pp. 140 et seq., whose disclosure is incorporated by reference herein). The compounded PVC mass is calendered at relatively low temperatures (150.degree..190.degree. C.)., i.e. is press-molded into a sheet by means of rolls; this sheet is not as yet thoroughly plasticized. In a second stage, the sheet, having only minor mechanical strength, is sintered by a short-term treatment as elevated temperatures and, in a further stage, it is refined by stretching.
Unmodified PVC can be processed only at low take-off speeds. It is desirable for economic reasons to increase the processing speed in the sheet manufacture of emulsion polyvinyl chloride according to the "Luvitherm" method without simultaneously impairing quality, and in particular, surface refinement, of the sheet stock.
The addition of small amounts of acrylate or methacrylate polymers has proved to be advantageous for improving the processability of polyvinyl chloride in general. Thus, it is known to utilize, as calendering aids, graft copolymers consisting of an elastomeric, non-crosslinked acrylic ester polymer as the graft base and methyl methacrylate, an acrylate and/or styrene as the grafting branch (DOS No. 2,135,024). However, the processability of emulsion polyvinyl chloride by the "Luvitherm" method cannot be improved with such graft copolymers according to the state of the art. See, e.g., DAS No. 2,624,656, column 2, lines 18-21.
DAS No. 2,624,656, on the other hand, describes mixed graft polymers which are characterized as suitable processing aids (modifiers) for vinyl chloride polymers to be used in the "Luvitherm" process. These mixed graft polymers are of a comparatively complicated structure and thus can be produced only with relatively great expenditures.